There currently exist many low production, or "stripper", oil wells in the United States and elsewhere in the world. The oil in these wells is not under the tremendous gas pressure commonly found in wells in new fields, and thus the oil must be lifted out of the well. The standard method for transporting oil from these wells is to use the "horse's head" or sucker rod pump commonly seen in oil fields in this country (see FIG. 1).
This type of pump is expensive to manufacture, install and maintain. A typical used pump assembly of this type can easily cost US $30,000.00. Additionally, this type of pump requires a large well servicing truck and rig for installation and for repairing problems in the down-hole portion of the pump assembly and in the tubing string. A typical well servicing vehicle costs, at the time of writing, approximately US $650,000.00 and weighs over 120,000 pounds. To service a conventional stripper well workers must erect a derrick that typically extends from 50 to 125 feet in the air and that is capable of lifting approximately three hundred and fifty thousand pounds of conventional steel tubing string. The installation and servicing of such pumps and tubing is both a costly and time consuming task.
It is generally known to those skilled in the art that conveyor ropes, belts, bands, strands, etc. (collectively hereinafter, "conveyors") can be caused to move along a predetermined path to convey materials. However, many of these devices suffer from a difficulty in maintaining the conveyor or belt at a sufficient and consistent speed to allow the effective transportation of materials. A "drive head" or "drive apparatus" for these conveyors is a mechanical or other means for exerting force on the conveyor, and ideally propels the conveyor through the system at a sufficient and consistent velocity. The drive apparatus in these prior systems often allow the conveyor or rope to slip as it is being propelled. This slippage causes additional wear and tear on the conveyor, causing costly delays while the transport mechanism is serviced to repair or replace broken or badly frayed conveyors.
Previous conveyor drive heads permit the conveyor to physically be lifted off the drive wheel(s) in the drive head due to centrifugal force, and in the case of systems transporting fluids, by hydroplaning due to the lubrication provided by such fluids, thereby causing the tractive effort to be insufficient to move the conveyor, and often resulting in its being abraded to failure. Certain prior art drive heads use one or more counterpoised wheels or belts to exert force by pinching the conveyor, either linearly or in a radial fashion, to induce traction, but these structures experience rapid wear of the conveyor due to internal abrasion. Further, all of these methods appear to be susceptible to "stalling" during which the conveyor speed drops to zero when the exit side tension drops to zero. Additionally, such many prior art drive heads suffer from being mechanically complex.
Heretofore, there has been no reliable and dependable mechanism for driving a conveyor along a predetermined path with relatively little slippage such that the conveyor consistently travels at a sufficient speed to transport materials dependably, has sufficient traction to draw the rope and fluids entrained therewith to the surface, exhibits a reduced rate of wear, and is mechanically simple.